Conventional passenger vehicles are of two types: two-wheeled motorcycles that lean into corners in what will be referred to herein as a G-force-neutralizing lean and four-wheeled cars that do not lean into corners in what will be referred to herein as a G-force-subject non-lean. Of course, those of skill in the art will appreciate that, below a certain cornering speed characterized by low G forces, motorcycles typically lean very little. Those of skill in the art also will appreciate that four-wheeled cars at sufficiently high cornering speeds actually tend to lean away from the corner and subject passengers to lateral forces. Finally, those of skill in the art will appreciate that a few three-wheeled cars are known including, for example, the British version of the Isetta (circa 1950s), which were characterized by the same G-force-subject non-lean as their four-wheeled counterparts.
Recently, a three-wheeled, one-passenger trike or motorcycle was described in U.S. Pat. No. 7,591,337 B1 entitled LEANING SUSPENSION MECHANICS to Suhre, et al. issued Sep. 22, 2009 and assigned to Harley Davidson Motor Company Group, Inc. The vehicle, which will be described herein as a trike, includes a frame, a rear drive wheel, conventional gasoline-fueled internal combustion engine, and two front wheels with a leaning suspension system. The suspension system includes one or more lean actuators configured to extend and retract to force-tilt the front wheels and to lean the motorcycle, responsive to a driver's pivotal rotation of the steering mechanism, e.g. the handlebars, through a corner. The actuators “are controlled by the leaning suspension control system that monitors at least one characteristic of the trike such as handlebar position (i.e. steering angle), speed, acceleration, etc.” Thus, the leaning of the trike described in the recent publication is understood to be actively controlled by the trike's leaning suspension control system, with said system applying a force to push the vehicle's center of gravity in the direction of the turn, thus leaning the vehicle into a turn, hereinafter referred to as ‘forced-leaning’.
This forced-leaning is very different from the leaning which occurs in a typical motorcycle, wherein the driver initially counter-steers (pushing the handlebars in the opposite direction of a turn), moving the contact patch of the front wheel out from under the vehicle, causing the vehicle to begin to naturally ‘fall’ into the turn due to gravity, at which point the driver adjusts the steering toward the direction of the turn as appropriate to maintain balance at a lean angle appropriate for the turn, speed, slope of the road, etc. This style of leaning is hereinafter referred to as ‘natural leaning,’ where the vehicle is ‘free to lean’ according to the driver's steering inputs, weight shifting, gravity, momentum and other forces.
Several leaning vehicles and concepts (such as the Mercedes LifeJet, the Persu (with technology licensed from Carver), the Clever, the Dagne, and the TTW Italia) use a complex system of forced-leaning or ‘active tilt,’ hydraulically (or otherwise mechanically) pushing the vehicle into turns, estimating the ideal lean based on speed and steering and other sensors. This forced-leaning approach presents three key challenges. First, it requires energy (reducing efficiency) for every turn, pushing (leaning) the vehicle such that a substantial portion of the mass of the vehicle is leaned into the turn—using the hydraulic pump or other mechanical means. Second, the timing difference (even tenths of a second) and imprecision in the forced-lean angle can make passengers feel queasy (like an amusement park ride). Third, the systems are complex and robustly built (as the vehicles are generally un-drivable without such systems), thus making the systems expensive and heavy (again reducing efficiency).
Mighell in U.S. Pat. No. 7,487,985 B1 entitled TILTING WHEELED VEHICLE issued Feb. 10, 2009 even more recently taught tilting idle or steering wheel linkage including kingpins at the ends of arms, the tilting linkages being within cylinders defined by the wheels' hubs. Mighell taught nothing about how to solve the problem of front-wheel oscillation.
In contrast, the free-to-lean design described herein enables the vehicle to lean smoothly and naturally, like a motorcycle, always on the correct lean angle, using no energy, and
it then gently holds the vehicle upright at stops and low speeds, using almost no energy. (Generally, when the vehicle is driven to a stop, the vehicle is already upright, such that the system only uses energy to close a hydraulic valve and hold the vehicle in the existing position (or applies very little pressure to adjust the lean angle a few degrees); this is analogous to the very limited energy a motorcycle rider uses when putting their toe on the ground at a stop to hold their vehicle in an upright posture.)
At very low speeds and on difficult terrain (such as steep driveways), the stand-up control system described herein dynamically keeps the vehicle upright adjusting to changing terrain. (Alternatively the system can also provide forced-leaning to lean the vehicle into a turn to match the so-called “G-forces” of such a turn. Those of skill in the art will appreciate that G-force as used herein refers to static and dynamic forces of gravitation and acceleration due to gravity or centrifugal forces such as those acting on a driver and his or her vehicle during straight-ahead, leaning, cornering, or accelerating operations.)
In the case of an emergency stop while leaning, the system has the power to stand the vehicle up from a full lean, allowing the driver to then resume driving.
The natural leaning vehicle described herein also has important advantages in ride smoothness and stability relative to forced-leaning vehicles. In forced-leaning vehicles, whether there are two wheels in the front of the vehicle, two in the rear, or two in both the front and rear, when a bump is encountered by a wheel on one side of the vehicle, the portion of the bump that is not absorbed by the suspension system is transferred into the body of the vehicle (because in forced-leaning, the angle of the body of the vehicle relative to the ground (and thus the wheels) is held in a firm setting). This means bumps are felt by passengers, and that the body of the vehicle has to be designed to constantly withstand such bumps, adding weight. It also means that the lean angle is disturbed, which can cause the vehicle to become unstable or even to tip over. In contrast, in the naturally leaning vehicle described herein, a bump encountered on one side of the vehicle is transferred to the wheel on the other side rather than into the body of the vehicle because the angle of the ground and wheels relative to the vehicle is free to change. Only a limited lift is transferred into the body of the vehicle. This free and natural leaning allows the vehicle to remain substantially in the preferred lean position for the current turn, speed, and terrain despite bumps and unevenness.